Session and header already sent problem

Please , I was using Wamp server before . I leter uninstall it and install XAMP. I now import my backup project, if I try to Login, it will show : session_start() [function.session-start]:Cannot send session cookie - header already sent by (output started at C:\xamp\... ...

That error message, which you cleverly truncated, tells you exactly where output started. Since you can't session_start() if output has already been sent then you need to fix the code so that doesn't happen.